Waves Through Earth: Interactive Online Mac and PC
This material is replicated on a number of sites
as part of the
SERC Pedagogic Service Project
Summary
This JAVA activity allows students to vary the seismic P and S wave velocity through each of four concentric regions of Earth. Students match "data" for travel times vs. angular distance around Earth's surface from the source to detector. Tabs are available for:
- P and S rays superimposed on the four-region model;
- Table of data for P and S wave velocities;
- Graph of "data" and Model for P and S waves;
- Help and instructions.
Learning Goals
Students can explore:
- Difference in P and S wave velocity;
- P wave and S wave shadows;
- Refraction;
- That S wave velocity must be zero for outer core to match observations;
- How to adjust model parameters to match observations.
Context for Use
Perfect for introductory geoscience course with Solid Earth content. Appropriate for students with a wide range of mathematical abilities.
Teaching Materials
Seismic wave Speed Through Earth (more info) has the complete activity. Click and drag the velocity lines at the top and bottom of each layer in the graph of Velocity vs. Depth to match the observed travel-time curves of times tab. [click image to enlarge]
Teaching Notes and Tips
Make sure to click calculate and check all tabs. This activity will likely take students about an hour to complete. Since it works on both Mac (at least with OS 10.2) and PC students should be able to do this as a homework assignment.
Assessment
Completion of the activity can easily be assessed by having students fill out the table provided here (taken from model tab of Applet) once they get their best fit. [click image to enlarge]
Examples of other appropriate questions are:
- What is the angular extent of the P wave shadow after wave speeds have been adjusted for best fit to data?
- Describe in your own words how wave speed changes with increasing depth towards Earth's center.
- Which waves travel faster, P or S waves?
- Perform a Google search (http://www.google.com) of P-wave and S-waves and in your own words describe what they are.
References and Resources
This Applet is one of several geoscience related Applets at Visual Entities
The Virtual Physics Laboratory of The Department of Physics and Astronomy at Northwestern University has a good animation of P (longitudinal) and S (transverse)waves.
